A small auxiliary power group, known in loving terms in the US Air Corps.

-It is a DC generator with 24-28 volts, 70 amps and 2,000 watts.

-It was designed as the HRU-28 and used in the aerial body for maintenance work.

-We clearly see that it is a two-stroke, single-cylinder engine.

"APU Electric Power Group"

-As is said on several occasions in this edition, aviation mechanics must be trained in the knowledge of the ground equipment entrusted to them, as well as in the aircraft engines for which it is prepared.